Information storage apparatus utilizing a record of internally reflective, light conducting material



3,177,476 NTERNALLY H. W. ROBINSON April 6, 1965 INFORMATION STORAGE APARATUS UTILIZING A RECORD OF I REFLECTIVE, LIGHT'CONDUCTING MATERIAL 2Sheets-Sheet 1 Filed May 29, 1961 INVENTOR. flaw/r; Wfim/soy Airmen/erApril 6, 1965 Filed May 29, 1961 H w. ROBINSON 3,177,476

INFORMATION STORAGE APPARATUS UTILIZING A RECORD OF INTERNALLYREFLECTIVE, LIGHT CONDUCTING MATERIAL 2 Sheets-Sheet 2 BMW) cam 75K f6f8 66 a INVENTOR. Han/4x2 h/flmum the clock track.

. 3,177,476 INFORMATION STGRAC-E APPARATUS UTILIZ- ING A RECGRD FINTERNALEJY REFLECTIVE,

LIGHT CUNDUCTHNG MATERIAL Howard W. Robinson, Bellrnawr, N.J., assignorto Radio Corporation of America, a corporation of Delaware Filed May 29,1961, Ser. No. 124,750 6 Claims. (Cl. 34tl-l74.1)

The present invention relates to apparatus for storing information on arecord, and more particularly to a system for identifying locations onthe record at which different information items may be stored.

' The invention is especially suitable for use in memory devices forelectronic data processing apparatus. However, features of the inventionare generally useful in the handling of recordable information in othertypes of apparatus.

' The location of information recorded at different places ona recordusually involves the use of a clock track. Pulses are recorded on theclock track in positions corresponding to the locations of differentitems of information recorded on the record. One or more signaltransducing heads are used, in addition to the heads which are used forreading and writing information, to scan Systems including the clocktrack recording and reproducing head or heads and their associatedcircuitry therefore add to the complexity and to the cost of datastorage apparatus.

Accordingly, it is an object of the present invention to provideimproved information storage apparatus in which the location ofdifferent items of information is facilitated at lower cost than was thecase with systems of the prior art.

It is a further object of the present invention to provide an improvedindexing system for different information storage locations on a record.

Briefly described, the invention may be incorporated in a recordtransport system utilizing a record constituted at least in part ofinternally reflective, light conducting material. The record may have aplurality of locations in which different items of information may berecorded (written) and from which different items of information may bereproduced (read). The light conducting material has an exposed portionwhich defines a track extending along the record. The track is marked soas to have one or more areas of different light transmissibility inpositions corresponding to the locations of the different items ofinformation on the record. A source of light is directed at the record.Light from the source is conducted through the light conducting materialof the record and illuminates the track. An index station is disposedalong the path of movement of the record and is exposed to illuminationfrom the track. Light responsive means are disposed at the index stationfor distinguishing between light and dark areas of the track. Signalsare generated by means controlled by the light responsive means at theindex station. Signals, such as pulses, are generated in response toeither the light or the dark areas of the track,

and are used to identify the locations of the different items ofinformation.

. the accompanying drawings, in which:

FIGURE 1 is a perspective view of a record transport and magneticrecording and reproducing system incorporating the invention;

FIGURE 2 is a block diagram of a circuit associated with the systemshown in FIG. 2;

r FIGURE 3 is a schematic diagram of a circuit for United States Patent0 3,177,476 Patented Apr. 6, 1965 controlling a record tracking armwhich is included in the record transport shown in FIG. 1; and

FEGURE 4 is a sectional view of a record of the type which may be usedin the record transport shown in FIG. 1.

Referring more particularly to FIG. 1, there is shown a deck plate illwhich supports the record transport. A turntable 12 is mounted on theplate l0 and is driven by a motor (not shown). A spindle 14 extendsupwardly from the turntable. A magnetic disc record 16 is disposed onthe turntable and is centered by the spindle M. The disc record will bedescribed in detail hereinafter in connection with FIG. 4.

A support member 20 extends vertically upwardly from the deck plate 10.A record tracking arm 18 is rotatably mounted on the support member 20.The arm 13 is one arm of a lever which may be raised and lowered by aneccentric drive mechanism 21. A crank arm 22 included in the eccentricdrive mechanism, is pivotally secured by a pin 24- at an eccentric pointon a drive wheel 26. A pin 23 extends from a rearwardly extending arm 54of the lever through a slot in the crank arm 22.

The drive Wheel 26 is mounted on a shaft 28. A spur gear 3%, driven byanother spur gear 32, rotates the shaft 28. The latter spur gear 32 isdriven by an electric motor 34 through a reduction gear box 36. Threecams 38, it? and 42 are mounted for rotation with the shaft 23. Followerarms 44 are actuated by the earns 38, 40 and 42. Switchesdd, 48 and 58are operated by the cam follower arms 44. The cams 38, 4t) and 42 willactuate different ones of the switches 46, 48 and 50 depending upon theangular position of the shaft 28. The cam 38 is shaped so as to actuatethe switch 46 when the tracking arm 18 is in its raised position. Thecam 40 is shaped to actuate the switch 48 when the arm 18 is in itslowered position. The cam 42 actuates the switch 58 when the arm is inan intermediate position. The maximum descent of the tracking arm islimited by an adjustable stop 52 which engages the rearwardly extendingarm 54.

The magnetic disc record 16, shown in FIGS. land 4,

includes a disc 56 having a central hole which receives the spindle M.The disc 56 also has a grooved hub 58, a web 60 and a rim 62. The discis formed of a material which readily conducts light and which iscapable of a high degree of internal reflection. Examples of materialswhich conduct light and which have a high optical index of refraction,and which are, therefore, suitable for the disc 56, are polycarbonateresins sold under the trade name of Lexan by General Electric Company ofSchenectady, New York, and acrylic resins sold by E. I. du Pont deNemours and Company of Wilmington, Delaware under the trade name Luciteand by Rohm and Haas Company of Philadelphia, Pennsylvania, under thetrade name Plexiglas. Materials of this sort can be either transparentor transluscent so long as they are light conductive and they have asubstantially higher optical index of refraction than the ambient (i.e.,air) whereby they are internally reflective. A disc 56 made of any ofthe above named or other materials of like optical properties has thecharacteristic of trapping, so to speak, light which enters it, sincethe light passing thereinto will be substantially total reflectedinternally except at certain surfaces of the disc which aresubstantially perpendicular to the light rays as, for example, at theedge of the disc along the rim 62.

The hub 58 of the record 16 is formed with spiral grooves 64 on theopposite fiat sides thereof. These grooves facilitate the entry of lightinto the disc 56, since they provide a greater surface area forreceiving direct illumination. The grooved surface also provides goodrep A .cam plate 102 is mounted on the slide 76.

felt, paper 1hr flock,-fare secured to the; opposite sides "orbetweenthe tape annuluses 66 and 68iand thebodies 72 of resilientmaterial. These pockets of air and the bodies ception for indirectillumination. The record'tracking arm 18 (FIG. 1) tracks in thegroovesl64. Layers70'of I adhesive-material are disposed onitheopposite, flatfsides of the webtl. Bodies 72 of resilient material, suchas" tserves' to block the. transmission ofnlight through the ina'rkedarea of the; rim. 'Andhde'x station'.114 is'.dis-

posed adjacentthejpath of'movement of therecord rimand is'exp'osed toillumination-from'the edge'of the rim 62. Themarked'rim constitutes atrack along the record edge which. parallels. the. record,trackwhich-isrecorded thereon.- A singleijs'piral 'record' track'ora-plurality of such tracks may berecordedu'sing a pluralityjof heads.

In operation, ais the .turntablezl2 rotates therecor'd 16,

i a forceradially inwardof the record is applied-to theguiding'stylus,SQJ-SinCethe;stylus'j8-6fand the' head 84 are mounted ona common: support, namely, the slide 76, the headfid follows the stylus86 and trackfthe spiral 72 of resilient material serve as a cushion foram'agnetic' 7 head. This type of record is more'fully described in thea-' copending application of E. A. Damerau and R. H; Jen

kins, Serial No. 198,810, filed May9, 1961, for InfOrmation StorageDevices'and Method of Making Samejia'nd g vrassignee as that of;the'present, in-

assigned; to the vention. t I i e I The tracking arm 18. has ajrecordtracking'assembly 74 which scans the record 1 6 for the purpose ofrecording spiral-record tracks on the-recording surface of the a 720ortwo revolutionsfof; the record. Bloeksofinfo'r jmatio'n'items maylbeilocatedonseparate successive turns,

disc record 16. Therecord tracking"assembly'includes' t v -ifdesired. Ineither case, the location of the different a slide 76 mounted on'a rod78. The slide 76 is stabilized by a stabilizing rod '81) which isengaged. by a roller82 The roller 82'isrotatably mounted on the topofthe slide, I r

76. v The slide is over-balanced about the'axis of the rod 78 so thatthe roller 82 is urged against the stabilizlingfrod 80. A stylus, 86 issecured in a block 88. The block 88 is pivotally mounted in abifurcatedarrn-90 Which'is,

pivotally mounted on a bracket'92 dependingfrom'thc slide 76.1f Thestylus adjusts itself in of its pivotal mounting.

a A magnetic head'84f contained in ablock 94; This I block 94ismountedin, an-arrn 96. The block 94.is mounted on a'pivot 109 forrotation'about a transverse axis. The arm ,96 ismounted in a mannersimilar tothe the groove'by virtue,

' recordtrackgin the? magnetic recording surface. of the record. .Forexample, twenty spirals may berecorded at ditierentfradial distancesfrom'the center of 'thereco'rd.

Each turn'bfthespiral track extends- 360 around the rec- "o'rd andcorresponds ,to one revolution thereof.v Different :1: itemsofinformation. constituting ablock of information .20

maybefrecorded onp'airs of successive't'racks. -In,other words, a blockv of information 'may be recorded around items of'informationcorresponds to, the number of. to;

't'ations ofv therecord 16. The'mark 112 on the illumi f nated edge ofthe disc w illpass the index station 114 once foreach rotation or turnof the record. The mark 112'is disposed impositionto correspond to thebeginning iof each turn; "Accordingly,vthe mark 112 corresponds posi:

' tionally with the jlocations tthe. turns of the record track) stylusarm 90. Accordingly, the magnetic head is subthe magnetic recordingsurface of the' record'ld,

cooperates with an actuating arm ltldofa switch 106.

whe'n the magnetic head 8 4 beginsto track the beginning of the spiralrecord track on the disc record 16. .'This I. switch 106 thereforeprovides information astolthe start (of data readingand/or writingoperations. a

This platel f {for the various items of: information on the record.

When the mark112passes thc index station 114, the beginning' of aturnlisiindicatedi Means 1are, disposed at the index station 114;which'distinguish the light anddark areas of the illuminated edge of therecord 16, and thereby detcct the passagejof thej mark 112; In someinstances,

more, than onemark 112 maybe provided on the-edge. stantiallyuniversally movable over limited distancesiso f oft e Iecofd (1130- Ythat the head may orient itself in. intimate contact with Referring moreI particularly to' FlG. 2', there is shown 7 suitable. photo-transistorknown; in the art, such as a The'cam plate 102is shapedso that theswitch .is'actuated type 2N46 9 [photo-transistor.-

This photo-transistor is responsive tothelig ht and dark areas. of theilluminated pedg'exof the record. 16: Theampliiier including this phototransistor' may be a class-A transistor amplifier 0t known design. Thisamplifier is biased to provide an i :o'utputsig'nal so longas thephoto-transistor is illumito the lamp have beeno mittedfrom'the drawingfor the sake of simplicity. The lamp 110 and the housing are.

disposed directly over the grooves-64in the hub 58 of the record 16. -Accordingly, light; rays from the lamp which are. shown by' the dashedlines in FIG. 1 are directed into the record through the hubportion-thereof; -As men-'- 'tioned above, the angularly oriented facesof the grooves i 64 facilitate the entry ofthe light rays into the disc56' of internally reflective,-lig ht conductive. material which con-'periencvmultiple internal reflectionsand thereby travel stitutes thecore of the-record 16. These'li'ght rays ex- 'nated'. When theillumination to the photo-transistor is 1 cut-01f, as-when the mark .112passes the index station 114,' the currentpthrough thephoto-transistoris temporarily interruptedf Then,.an output pulse-of voltage, which ishigher. thanjthe voltage normally provided at generally in a lateraldirection throughthe hub- 58 an'd 1 the web '60 to the rim 62' of'therecord. All light raysexcept those which are'substantially perpendicularto the edge surface of the disc rim 62 aretotally reflected, since theindex of refraction of the disc is much greater than the index ofrefraction of the airprthe'layer '70of adhesive material which coversthe'web 60 e-Only theredgeof the record at the rim62,is illuminated,since this edge is substantiallyfperpendicular to the light rays fromthelamp .1

whichare trapped within'the disc 56; i r

{The edge of the rim 62 is marked by a'spot'11'2.' I I 7 spot ormark-maybe formed by-opaque paint on, or an insert ofopa'quemat'erial'in, the rim:62. The mark 112 the output of thephoto-transistor amplifier,isgenerated and'i's applied to a mono stablemultivibrator (one-shot) 118V A capacitive coupling may be'usedbetweenthe photo-transistor amplifier 116 and the-mono-stablemultivibrator 118 so that only the pulse corresponding to" the markedareaof 'the record edge will bev applied to the multivi-bratorfand the'slowvariation's in D.C. level will be blocked. The output of themultivibrator is a pulse 7 of predetermined duration The' mono-stablemultivibrator 11'8is triggered by the leadingedg'e'of the :pulsefrom.the photoetransistor amplifier." 'Accordingly, the

size ofthe mark 112 will 'not be critical and'the pulse providedby'themono-stable*multiyibrator will be of'a durationand shapesubstantially' independent of the shape of the mark 112 andther-shape-of the pulse provided'by the photo-transistor amplifier 116,YIt is also desirable that the multivibrator 118 have a predeterminedt-hreshold triggeringslevel. Imperfectionsin the disc" and foreignmatter, which might imodify'the illumination of ',-the edge of therecord, 'may cause the output of the photo-transistor amplifier to varysomewhat, when areas revolutions.

formation in individual turns.

other than the mark 112 pass the index station 114. Such noise or discimperfection produced signal variations will. not be of suflicientamplitude to trigger the monostable multivibrator 118. The output of thernultivibrator 118 is applied to an AND gate 120. Anotherinput isconnected to the AND gate 120 from a source of operating voltage through.the switch-106. The AND gate 120 will be enabled only when the switch106 is closed. It was pointed out in connection with FIG. 1 that theswitch 106 is actuated only when the magnetic head is in record trackingposition. In practice, it may be desirable to provide lead- -in groovesfor the stylus 86 and corresponding lead-in tracks for the head 84 whichextend over one to three The cam 102 actuates the switch 186 at thebeginning of the first turn of the record track, or after the end of thelead-in tracks. Output pulses correspending to the pulses generated bythe mon-stable multivibrator 118 will be transmitted by the cam 120 onlyafter the beginning of record tracking operation.

The pulses passed by the gate 120 are applied to the for reading from orwriting on any block of the record track may be enabled at the properinstant to transfer information from any desired location on the record10.

- ,Ablock of information in the system illustration herein is containedin a pair of successive turns of the record track. It may be desired towrite different blocks of in- In the latter case, it will be desired tocount each record track. Accordingly, the binary counter may responddirectly to the output of the gate in the event that individual turnsare counted. The binary counter is reset after all of the record trackson the record are scanned. For example, the record 16 may have twentyrecord turns divided into ten blocks. The

mark 112 will pass the index station at the beginning of each turn. Themono-stable multivibrator 118 will generate twenty pulses, each in timesequence. Each odd pulse will be counted by the binary counter 124. Whenten pulses are counted, the binary counter will provide an output.

This output will be fed back to reset all the counter stages to zero. I

The record transport system shown in FIG. 1 is adapted I to beassociated with a record holder which contains a plurality of differentrecords. Each of these records will be identical to the record 16.Record transfer means, such as disclosed in the Vanderzee et a1. PatentNo. 2,697,607, issued December 21, 1954, may be provided to transferrecords selected at random to the turntable 12.

A system is shown in FIG. 3 for controlling the raising and lowering ofthe arm 18 so that a record may be transferred from the turntable 12 tothe basket and a new record placed on the turntable and scanned by thehead 84. The cams 38, 40 and 42 are used in this system. However, forthe purpose of simplifying the 7 discussion and the circuitry involved,while adequately explaining the mode of operation of the invention, thecam 42 and its associated circuitry which responds to the intermediateposition of the arm has been omitted in FIG. 3. The arm is raised andlowered by the motor 34. This motor may be a direct current motor havinga field winding 126 and an armature 128. The motor .is controlled by arelay 130. The contacts 130a of this relay are connected either to shortcircuit the armature 128 or to connect ground to the armature. In thelatter case, armature current will flow and the motor will rotate. Motorrotation is unidirectional. The eccentric 26 and the crank arm 22 changethe unidirectional motor rotation into reciprocating motion for movingthe arm up and down. The circuit is shown in FIG. 3 with the switches inthe positions assumed when the arm is raised to its maximum upper-mostposition. A relay 132 is energized when the arm is to be disposed inlowered position for scanning the record'16. Another relay 134 isenergized when the arm is to be disposed in raised position. Theserelays 132 and 134 operate relay contacts 132a and 134a, respectively,The cam 38 operates the switch 46 only when the arm 18 is in raisedposition. The cam 40 operates the switch 48 when the arm 18 is inlowered position. Since the arm 18 is connected to the motor 34 throughspeed reduction gearing, the arm will remain in its assumed positionwhen the motor '34 stops.

For the situation where the arm is raised, as shown in FIG. 3, acircuitfrom B+ to the motor control relay is broken at the cam operatedswitch 46. The motor control relay 130 is therefore de-energized. Thearmature 128 is short-circuited and therefore dynamically braked.Accordingly, the arm remains in raised position until a command isreceived from a user equipment, such as .a computer, directing the armto move downwardly into position to scan the record 16. Upon suchcommand from the computer, the relay 134 is de-energized and the relay132 is energized. A circuit is completed to the motor control relay 130through the contacts 134a, which drop-out, the cam switch 48 and thecontacts 132a, which pull in, to ground. Current then flows through thearmature 128 and the motor turns. The motor 34 continues to turn untilthe switch 48 is opened by the cam 40. The motor control relay 130 isthen de-energized and its contacts 130a drop-out. The motor 34 isdynamically braked through the contacts 130a so that the arm remains inlowered position in scanning relationship with the record.

When the user equipment commands the arm to move to raised position, therelay 132 is de-energized and the relay 134 is energized. A circuit isthen completed to the motor control relay 130 through relay contacts134a and the cam switch 46. The motor turns until the cam switch 46opens. When the motor stops due to electrodynamic braking, the arm 18remains in raised position until another command is received from thecomputer to lower the arm.

From the foregoing description, it will be apparent that there has beenprovided an improved information storage apparatus having an improvedindexing system for locating items of information which are stored indifferent locations on a record. While the invention has been describedin connection with a disc record transport and handling system, it Willbe appreciated that features of the invention are useful with othertypes of record members. Variations in components of the illustratedsystem and in the system itself, all within the spirit of the presentinvention, will undoubtedly be apparent to those skilled in the art.Accordingly, the foregoing description should be considered asillustrative and not in any limiting sense.

What is claimed is:

1. In a record transport system in which a record travels along a path,said record being constituted at least in part of internally reflective,light conducting material having an exposed portion which defines atrack extending along said record, said track having areas of diiferentlight transmitting properties, an indexing system which comprises anindex station disposed along said path and exposed to illumination fromsaid track, a source of light directed at said record for illuminatingsaid material and thereby illuminating said track, means disposed atsaid index station for distinguishing between light and dark areas ofsaid track, and signal generating means responsive to said light anddark area distinguish- 'ing means for, generating asignal whieh variesiaecord ancewith said-light and dark; areasl a ame is a 7 Itw'een isaidflight;v and: dark: areas iof saidledge which .pass said indexstatiom P Ii =2., co a i n,a ec ,i i]. -s Q g fli fa 1 1n; j i nat Qn,'- :.Ji'i agti d s lf srd iwhi h 3 ralityaof items:ofinformationatapluralitygofdisereje comprises lad i sc finternally"refleetive,ilightgjconduetivelocations thereon; said ;record; being; constituted in part n i-ateria lhaying j'an annjilusof 'magnetio tape secured-to the surface saidloeations.being marked so as to have difierent light'i grecord trackion'said tape annnlus theedge o f'isaid diso a ss itw ea f d m ngjg v ino'saidjrecord, being marked at a portionffihereof in' erito transanindexingvstation located to .be exposed to illumination-1 mit lig'htdiifere'ntlyithan thatf m m fi a elh'1f0ugh}.the from said portion,means for moving said record past 'sald jg" rest of said diseedgefa'lamp onsaid arm 'ior directing said indexing station' indexingstation, and means for distingnishingjbetvveen light into.; s'aiddiseflwherebytogilluniiilatersaid edge an light and dark areas of saidlfrecord" "ortion whlehflpasses inden station, disposed ';adjacent: to,said edge, a; turntable for rotait'ingasaid' record relative tojsaidarm, and means f n, r y a m ne un d on said armffor scanning successivespiral turns of 1a.

.3. In cornbinatiomja discf eeord, aY lg; 5 7 2;f rv fir at saidindexgstation fol distinguishingbetween light and tplura lity of itemsof informationI-at.a pljlralitvpf" 106 a:- Jdark areas of. saidedge'whic hjass' said indegg stationp tionsspaoedradially v vithrespec tto'eaohl' other tgon' saldf a I 6 In n'iagnetici,reeordi g andfreproducing; apparatus,

record, said.v record being, c0n'sti tuted part of ja disc 1 thecombination comprising a magnetic' dise' reeor d in,- of internallyreflective, lightlcondnctive materiaLjthe Q clndingfazdiseoffinternally},refleetive light: condngtive peripheral edge of saiddisohavingat least-forte area there;- 7 material, the dge of-saidrejeord' b eing marked at appr of in aj'position corresponding to said,locations'niarke'd tion thereof to .ehangei the transmissionof light the-..

to have different light tr'ansmi'ssion than. the rest of said I I ithrough from that throughthe v restfoflsaididi edgeg a edge, meansfor'jdirecting'ligh t into said disc to;-il1nmina tel, magnetic head fortr kin ajzspiray mcorditrack on :Siaivd said edge,'lanfindexingfstationexposed to illumination v I 7 from Said edgei-meansf l r i S i W QT S0 h f recor d,j jeans for direc'tingdight inte -saidrecordffor 7 said edge revolves past said indexing station,;.and means-Qill inating s id edge thereof,andimeans jfor "identifyfor distinguishingbetween the light; and dark areas of: '*.ing t he o ne of said"recordtracksbeing scanned bysaid saidedge vvhich pass' said indexing-,station. f head'gxvhich comprises [an indexing station exposed to Igrecord as said record rotates, means; for rr tating said 4., Incombination, a diserec'ord having a' lreeord trael; ill'uimingtrilan ffol id' eq n ht i i y i having a pl i y 'of rns" sp 9ed "r a yfr m e chsaid, indeidi station-tor; rovidin a ulse when said other, saidreco'rdjalso having a groovedhub and .c om-' arkipasses saidjindexingstation,and means ooupled '7 7 record, means for directinglightintosaid hub to ill'u' i I nate said -edge,; an index station locatedto. be exposedprising a disc of internally reflective, light'oondiictive to,saidilightresponsiveln eansionconnting said' pnlses.

material extending-radially to the peripheral: edge ofsaid I fffRelference's' Examiner- I; v

r v J'UN'ITEDQSTATES ;PATENTS, 1v

"to illumination from oneedge, said'gedgehavinganarea y g V g l a in aposition corresponding to theHstart-ofeachof said I gm "Y- 7 turns,through-which the transmission oflight 'is difierg 9 P Md 1 3 e'nt thanthat through the rest,of sa dedge, I eansfor IRVIN B g tta-Examiner}. v

- rotating said'record soLthat' said'edge passes-saidgindex ,0

station, and'means at said station for"distinguishingbe-f

1. IN A RECORD TRANSPORT SYSTEM IN WHICH A RECORD TRAVELS ALONG A PATH,SAID RECORD BEING CONSTITUTED AT LEAST IN PART OF INTERNALLY REFLECTIVE,LIGHT CONDUCTING MATERIAL HAVING AN EXPOSED PORTION WHICH DEFINES ATRACK EXTENDING ALONG SAID RECORD, SAID TRACK HAVING AREAS OF DIFFERENTLIGHT TRANSMITTING PORPERTIES, AN INDEXING SYSTEM WHICH COMPRISES ANINDEX STATION DISPOSED ALONG SAID PATH AND EXPOSED TO ILLUMINATION FROMSAID TRACK, A SOURCE OF LIGHT DIRECTED AT SAID RECORD FOR ILLUMINATINGSAID MATERIAL AND THEREBY ILLULMINATING SAID TRACK, MEANS DISPOSED ATSAID INDEX STATION FOR DISTINGUISHING BETWEEN LIGHT AND DARK AREAS OFSAID TRACK, AND SIGNAL GENERATING MEANS RESPONSIVE TO SAID LIGHT ANDDARK AREA DISTINGUISHING MEANS FOR GENERATING A SIGNAL WHICH VARIES INACCORDANCE WITH SAID LIGHT AND DARK AREAS.